1. Field
The present invention relates to a nonaqueous-electrolyte battery.
2. Description of the Related Art
Nonaqueous-electrolyte batteries which are charged/discharged based on the movement of lithium ions between the negative electrode and positive electrode are being extensively investigated and developed as batteries having a high energy density. Nonaqueous-electrolyte batteries employing a lithium-transition metal composite oxide as a positive active material and a carbonaceous substance as a negative active material have already been commercialized.
On the other hand, nonaqueous-electrolyte batteries employing a material having a higher lithium insertion/release potential than carbonaceous substances, such as, e.g., a lithium-titanium composite oxide (about 1.55 V vs. Li/Li+), as a negative active material are being investigated in recent years (see, for example, Japanese Patent No. 3866740 and JP-A 9-199179). Lithium-titanium composite oxides change little in volume with charge/discharge and hence have excellent cycle characteristics. Such nonaqueous-electrolyte batteries are theoretically free from lithium metal deposition and can hence be charged at a high current.
It was found that in the battery employing such a material having a high lithium insertion/release potential, e.g., a lithium-titanium composite oxide, as a negative active material, a reaction accompanied by gas evolution occurs within the battery due to the battery reactions or during long-term storage. Due to this reaction, the battery deteriorates in battery characteristics such as high-current characteristics and self-discharge characteristics.